The present invention relates to a blower beater mill for grinding and drying. A rotor comprises a beater portion and a fan impeller both located on the mill shaft. The beater arms of the beater portion are fastened between hub rings of the mill shaft. The mill shaft is water-cooled along its longitudinal axis.
Such mills, for drying wet material to be ground, suck hot flue gases through a suction duct from the firing chamber of the boiler. Hence the rotor is subjected to a high temperature load during the grinding-drying process and during startup and rundown.
It is known how to cool the mill shaft over an inside bore-hole. Also, the mill shaft in the area of the entry cross-section of the mill can be enclosed with a shaft protection tube, with cooling air being conducted through the space between shaft protection tube and mill shaft.
With a known blower beater mill whose mill shaft is not equipped with an inside borehole for water cooling, the cooling air passing between shaft protection tube and mill shaft is passed through cooling channels located between the hub of the rotor and the shaft. In order to achieve adequate cooling of the mill shaft in this blower beater mill, large cooling air quantities must be passed through these cooling channels. Nevertheless, the mill shaft gets relatively hot so that the mill shaft cooled in this manner is inferior to a mill shaft cooled with water through an inside borehole.
It is, therefore, an object of the present invention to protect the mill shaft of a blower beater mill of the above type, in such a way, that high temperatures on the shaft crest and the temperature differential across the shaft cross-section are reduced.
Another object of the present invention is to provide an arrangement of the foregoing character which may be economically fabricated and readily maintained in service.
A further object of the present invention is to provide an arrangement, as described, which has a substantially long operating life.